V. hot brake caliper

[Martin Barrett]

I inspected my pads last week, the rears just needed a clean up. The plastic cap was slightly distorted. I think that was from last year when my pads were only lasting 5,000 miles or less, and was traced to a sticky pedal pivot, since that was cleaned and greased they've been great. During that time I'd run them down to the backing pad twice and had to make a conscious effort having backed the pads back not to use the rear brake on the journey home.

 

The easiest way is clean it up, new fluid and go out and do some test stops and see how it is. Most of your stopping is done on the front, so fairly safe if have a complete failure on the rear. If the seals leak replace them. If not carry on.

[Guest ratchethack]

. . .Most of your stopping is done on the front, so fairly safe if have a complete failure on the rear. If the seals leak replace them. If not carry on.

Martin, there's been at least one poster on this Forum that I know of, and one LM rider I rode with on the day it happened, whose rear brake failed completely, then locked up on the road from lack of proper care & attention (the Big 3 again, as noted above).

 

So I take exception to the statement that it's "fairly safe if [you] have a complete failure on the rear."!!!

 

Neglect here can (and HAS repeatedly) put riders in a ditch at a time and place not of their own choosing.

 

By all means pay careful attention to the Big 3 -- THEN carry on -- with confidence!

[dlaing]

Um, from repeat previous experience, I assume this is not suggested in jest.

 

It would be an OEM first for all terrestrial vehicles I know of on the planet.

 

How many G's of downforce from hitting a bump (that is, assuming Earth gravity) d'you s'pose it would take to hold the relief port in the master cylinder closed (for many minutes!), let alone get the rear brake to drag??

 

Now this is just me, but considering the Physics involved, and applying a little elementary logic and common sense, it would hardly seem likely that "hitting a bump" would:

 

1. generate anywhere near sufficient downforce on the brake lever to cause the leverage of its tiny mass (the "massive brake lever" weighs only a few ounces, and it's just several inches in length) to first overcome the master cylinder return spring, let alone apply some number of pounds of downforce long enough to cause any dragging, let alone (Part II) consistently enough to cause heating of the caliper?? Would it be enough force if the "bump" required to do all of this (wot a walloping "BUMP" it would have to be even to do it for an instant!) create a large enough impact force to bottom both front and rear suspensions hard enough to break the frame and shatter the fork stanchions. . .??

 

2. Assuming that the impact to the chassis of hitting a "bump" COULD depress the lever enough to counter the master cylinder return spring, hold the relief port closed for a period of time long enough to build more pressure from heat, AND actually get the brake to engage, how could any kind of a momentary impact -- or (considering even well beyond the earthly realm of extreme possibilities) even a series of impacts, say from bottoming-out the suspension repeatedly over mile after mile of continuous deep, suspension-bottoming whoopers -- ever result in a sustained enough depression of the lever to replicate any downforce on the brake lever even close to that generated by the shortest application of the rear brake in normal brake use -- let alone drag the pads long enough to start a heat/drag cycle??

 

To suggest the above would seem the equivalent of suggesting that hitting a bump with a car could cause the mass of the car's brake pedal by itself to apply the brakes hard enough and long enough to cause brake fade. . . Maybe the force of a free-fall drop off a couple hundred foot cliff would do this for a split second? Repeatedly dropping off multiple cliffs for several minutes, long enough to hold the brake pedal down so that the brakes overheat??

 

Where's Wiley E. Coyote and the Roadrunner?

 

Rapt once again in wonder and amazement , enquiring minds (well, you know). . .

Here is BFG's brake lever

[Guest ratchethack]

Here is BFG's brake lever

Err, and. . . . ??

 

Dave, you must realize that until the above post, many Forum members were no doubt convinced you were joking.

 

I, of course, know better by now. . .

 

Truth be told, I don't know f'er sure if BFG used depleted uranium to fabricate his Most Masterful Bodge or not .

 

But I b'lieve if he DID use this most massive element on this planet , instead of a few ounces of wot appears to be aluminum (aluminium as BFG knows it ), it wouldn't make any more difference to the liklihood of the most horrific "bump" encountered by BFG's Guzzi causing any slightest possible movement of the brake lever, than a seagull landing on deck would cause the sinking of the SS Norway . . .

[dlaing]

Um, from repeat previous experience, I assume this is not suggested in jest.

You are correct

It would be an OEM first for all terrestrial vehicles I know of on the planet.

Obviously BFG's Bodged Fulcrum Girder is not OEM

How many G's of downforce from hitting a bump (that is, assuming Earth gravity) d'you s'pose it would take to hold the relief port in the master cylinder closed (for many minutes!), let alone get the rear brake to drag?? huh2:

How could the force of hitting a bum hold the relief port closed?

For it to be held open the girder would probably have to weigh just about 1.5kg.

I put a 2# weight on the toe of my lever and that was enough to close the relief port.

I doubt that his girder is that massive but it may well be over a kilogram. huh2:

What can happen is that if the return spring is weak enough and the bodged fulcrum girder is massive enough, the brake could be momentarily activated when bumps in the road were met.

Repeatedly this could cause overheating and failure.

 

 

Now this is just me, but considering the Physics involved, and applying a little elementary logic and common sense, it would hardly seem likely that "hitting a bump" would:

 

1. generate anywhere near sufficient downforce on the brake lever to cause the leverage of its tiny mass (the "massive brake lever" weighs only a few ounces, and it's just several inches in length) to first overcome the master cylinder return spring, let alone apply some number of pounds of downforce long enough to cause any dragging, let alone (Part II) consistently enough to cause heating of the caliper?? whistle: Would it be enough force if the "bump" required to do all of this (wot a walloping "BUMP" it would have to be even to do it for an instant!) create a large enough impact force to bottom both front and rear suspensions hard enough to break the frame and shatter the fork stanchions. . .??

 

2. Assuming that the impact to the chassis of hitting a "bump" COULD depress the lever enough to counter the master cylinder return spring, hold the relief port closed for a period of time long enough to build more pressure from heat, AND actually get the brake to engage, how could any kind of a momentary impact -- or (considering even well beyond the earthly realm of extreme possibilities) even a series of impacts, say from bottoming-out the suspension repeatedly over mile after mile of continuous deep, suspension-bottoming whoopers -- ever result in a sustained enough depression of the lever to replicate any downforce on the brake lever even close to that generated by the shortest application of the rear brake in normal brake use -- let alone drag the pads long enough to start a heat/drag cycle?? huh2:

 

To suggest the above would seem the equivalent of suggesting that hitting a bump with a car could cause the mass of the car's brake pedal by itself to apply the brakes hard enough and long enough to cause brake fade. . . Maybe the force of a free-fall drop off a couple hundred foot cliff would do this for a split second? Repeatedly dropping off multiple cliffs for several minutes, long enough to hold the brake pedal down so that the brakes overheat??

 

Where's Wiley E. Coyote and the Roadrunner?

 

Rapt once again in wonder and amazement , enquiring minds (well, you know). . .

It all boils down to the mass of the lever and return force of the spring.

I suspect a repeatedly bumpy road would cause the overheating and not one dip of a pothole.

I would not ride that bike with that baked seal.

I would not ride that bike with that brake lever, if it weighs as much as it appears to me.

I'd feel safer with no rear brake, BAA,OMHO

I can only lead a horse to water...

[mike wilson]

The metal must have been dragging on the disk during the long run home, because when I went to change them later, the black plastic cover was gone – all that remained were lumps of melted plastic. Must have been hot!

Has anyone else seen this happen?

 

I've seen many warped and bubbled covers from Brembo calipers but this is the first total melt. I think you can award yourself a gold star.

 

 

 

 

 

 

Or maybe a thruxton.

[jrt]

You might check to see that the brake line isn't routed too close to that exhaust box.

[dlaing]

Looking at that picture, the free-play is set to zero or less.

If less than zero, that could have caused the problem.

The advantage of freeplay is that you can visually ensure you have no negative free-play.

I suppose the disadvantage of more free-play is that a heavy lever like that could develop more momentum, so it may good for BFG to minimize the free-play.

[Dan M]

Here is BFG's brake lever

 

Not likely thers's enough weight in that lever to apply the brake. The internal spring in the master has considerable force. It may be that the lever return stop or linkage is out of adjustment and there is no free-play. This coupled with heat expansion can cause dragging.

 

I agree with Ratch that a rear brake failure can be dangerous. While I do 90% of my stopping with my front, and the likelyhood of a rear failure is remote, and I think I'd notice if it were dragging before things got hairy. If the seals failed from severely overheating and dumped brake fluid on my rear tire, that may be cause for concern.

[dlaing]

Not likely thers's enough weight in that lever to apply the brake. The internal spring in the master has considerable force. It may be that the lever return stop or linkage is out of adjustment and there is no free-play. This coupled with heat expansion can cause dragging.

 

I agree with Ratch that a rear brake failure can be dangerous. While I do 90% of my stopping with my front, and the likelyhood of a rear failure is remote, and I think I'd notice if it were dragging before things got hairy. If the seals failed from severely overheating and dumped brake fluid on my rear tire, that may be cause for concern.

I think we all agree that a rear brake failure can be dangerous.

But I disagree that you'd be likely to notice the dragging before bad stuff happens.

[Guest ratchethack]

How could the force of hitting a bum hold the relief port closed?

Well, it couldn't, Dave. That's exactly my point. Without some additional force holding the relief port closed, and beyond this, dragging the pads for some period of time, there's NO WAY ON THIS PLANET that hitting a bump, by itself, could either start, or contribute to the heat/drag cycle, as you've suggested. A more reasonable (and maybe more interesting) question to ask might be: Could hitting a bump by itself have an effect on the movement of the (otherswise unassisted) brake lever strong enough to first overcome the return spring enough to close the relief port at all -- even for an instant??

. . .

I put a 2# weight on the toe of my lever and that was enough to close the relief port.

I doubt that his girder is that massive but it may well be over a kilogram. huh2:

What can happen is that if the return spring is weak enough and the bodged fulcrum girder is massive enough, the brake could be momentarily activated when bumps in the road were met.

Repeatedly this could cause overheating and failure.

Not as massive as 2 lb., but "it may well be over a kilogram"??!!

 

Um, a kilo is 2.2 lb., Dave.

 

But let's concentrate on your words above, "momentarily activated" and explore this a little, shall we?

 

[. . . sigh . . .] Somebody's just gotta do it. . .

 

Dave, first let's make every attempt to be reasonable here, please. I'll make my best honest effort, and I'd appreciate the same. You say you've put weight on the end of your brake lever to determine what it would take to close the relief port. That's fine, and I'm willing to take you at your word on this, but I'm not buying anything remotely close to a kilo (depleted uranium is expensive!!) for your speculation as to what BFG added to his lever, and of course you had no way to measure this as you said you did the 2 lbs. it took to overcome the return spring. Now I'm not likely to disassemble my brake and weigh the components for purposes of this argument. However, I b'lieve we can make valid estimates here that point to reasonable conclusions.

 

I've had all these parts in my hands separately more than once for routine service, and I'm pretty confident in saying that the stock brake lever assembly weighs in the neighborhood of a few ounces total. Let's say 3 oz. Some of the weight of the aluminum lever is offset as measured at the end of the lever -- in part -- by aluminum and additional steel linkage parts on the other side of the lever's fulcrum. That is, gravity and increased G-force effects from a "bump" on the forward end of the brake lever is cancelled out, in part, by the weight of the lever assembly components behind the fulcrum. When the lever is depressed off its resting point, this includes the weight of the piston in the master cylinder, which is of course directly linked.

 

As you've pointed out, and further speculating only for purposes of illustration, if BFG had used the aforementioned depleted uranium for his "splint", he may have raised the weight (and mass) of the lever considerably. Somehow I rather think he used mostly aluminum, possibly with a smattering of other premium bodgery materials. So (being generous here) he may have put as much as an additional ounce of weight as measured at the forward end of what (in total) might now weigh as much as a whopping 3 ounces (yes, I'm considering the steel screw that fixes the rubber pedal, and the pedal itself!) Round figures, I'm estimating (again, being quite generous) that BFG has the equivalent of a total of 2 ounces of normal gravity downforce as measured at the end of a lever arm located ahead of the fulcrum that is not offset by the weight of the lever assembly, linkage, and piston on the other side of the fulcrum. I reckon a postal scale under the lever would be just the thing, and this'd be the end of the story.

 

Now then. If you're accurate in your assessment above in saying that 2 lbs. downforce is what it takes to close the relief port, the question now becomes:

 

How many G's of downforce from a "bump" would it take to get 2 oz. measured at the end of the lever to overcome 2 lbs. of return spring force and close the relief port?

 

Since 16 ounces = one pound, and we have 2 lbs. to overcome, it would take 16 G's of downforce just to reach a balance. So I reckon it would take 17 G's or so to close the relief port, and based on feel, possibly upwards of an additional 2 lbs, or another 17 G forces beyond this to actually apply enough pressure to get the brake pads to grip the disk even enough to be detectable at the brake caliper, let alone generate any measurable heat and stopping force at all.

 

Now Dave, how well d'you think the V11 Guzzi by itself, weighing in the neighborhood of 550 lbs (round figures), would tolerate hitting a bump of a magnitude that would generate 17 G's? 17 G's would make the Guzzi weigh 9,350 lbs., or 4.7 tons.

 

As a rider, assuming you weigh 200 lbs. (round figures), how well d'you think YOU would tolerate 17 G's? 17 G's would make you weigh 3,400 lb, or 1.7 tons. How well d'you figure you could tolerate this kind of a "bump" without a G-suit? I b'lieve there are some experienced fighter pilots who can briefly tolerate 8 or so G's without blacking out without a G-suit, IIRC. But how about more than DOUBLE that?!

 

The combined weight of Guzzi and rider at 17 G's would be in the neighborhood of 6.4 tons. Setting suspension considerations aside, how well d'you figure the tires would handle this kind of a "bump"? My Metzeler Z6 rear is rated for a max of 716 lbs. and the Z6 front is rated at a max of 520 lbs., for a total vehicle maximum tire capacity of 1,236 lbs., or .6 tons.

 

So wot you've suggested here, Dave, is a "bump" that would overcome the brake return spring of a magnitude -- just enough to close the relief port, mind you -- of 10.6 times the combined maximum load capacity of Metzeler Z6 tires.

 

Now THAT, my friend, is one walloping, horrific and hellacious BUMP! And this doesn't even apply the brakes! To apply the brakes enough to engage the pads, you'd have to DOUBLE THIS!

 

D'you think these numbers support your conclusion?

 

Well of course not, silly. Why even ask?! More'n likely , of course, you think my numbers are off by at least an order of magnitude!

 

So with the assumption already safely made that I'm wrong, exactly where d'you now suggest that I've made my mistake(s), Dave?

 

Enquiring minds (well, you know).

[Martin Barrett]

I still think it would be fairly safe to reassemble and road test.

 

A couple of applications stop and inspect.

 

If the seals are shot - fluid will leak - fairly obvious stop testing and replace

If the seal are shot and the pads are dragging the disc will get hot , ride a bit without using it and again test for heat. It's a known suspect area so ride accordingly. If seems well increase the inspection distances

 

Should get enough advance warning not to suffer the dangerous seizure.

 

But if stopped by the police don't say you're conducting tests on your defective brakes.

[Dan M]

I still think it would be fairly safe to reassemble and road test.

 

A couple of applications stop and inspect.

 

If the seals are shot - fluid will leak - fairly obvious stop testing and replace

If the seal are shot and the pads are dragging the disc will get hot , ride a bit without using it and again test for heat. It's a known suspect area so ride accordingly. If seems well increase the inspection distances

 

Should get enough advance warning not to suffer the dangerous seizure.

 

But if stopped by the police don't say you're conducting tests on your defective brakes.

 

 

I agree with all of this Martin. When inspecting the caliper it will be obvious if there is trouble before reassembly. (condition of visible dust boot, how smoothly the piston retracts...)

And yes contrary to popular belief if any brake is dragging enough to overheat, it would be tough not to notice before it got so tight as to cause catastrophe.

[guzzijack]

I agree with all of this Martin. When inspecting the caliper it will be obvious if there is trouble before reassembly. (condition of visible dust boot, how smoothly the piston retracts...)

And yes contrary to popular belief if any brake is dragging enough to overheat, it would be tough not to notice before it got so tight as to cause catastrophe.

 

Er, is there a dust boot on the caliper? I thought there were twin seals on the piston but no dust boot. And BTW if the teflon type coating on the piston has lifted slightly due to heat or one of the seals hardened for the same reason, it is possible for the brake to drag enough to overheat and not be noticeable - or is my Centauro so much more powerful than a V11S that it overcame it

(flak jacket on )

 

GJ

[Guest ratchethack]

And yes contrary to popular belief if any brake is dragging enough to overheat, it would be tough not to notice before it got so tight as to cause catastrophe.

Dan, I agree that "popular belief" is often misleading at best, and flat-out wrong at worst, as I'm sure is your point.

 

But again, FWIW, I've seen with my own eyes, up close and personal, a seized rear brake on a V11 Guzzi that was (evidently) not noticed until the brake let go, just before locking up on the road while underway. Fortunately the rider didn't dump it, as it had slowed the bike down against his efforts to "ride it out" with lower gears and more and more throttle!

 

Again, at least one other poster on this Forum has admitted to what sounded like exactly the same thing.

 

I also agree from my own perspective that it'd be mighty tough for Yours Truly, and I suppose lots of others, not to notice that something's wrong in this situation and take corrective action long before the situation became dangerous.

 

But then, that's just me, and of course anyone else's MMV.